Collision mitigation apparatus

ABSTRACT

A collision mitigation apparatus includes an object detecting section for detecting a collision object present in front of an own vehicle on which the collision mitigation apparatus is mounted, a drive assisting section that performs drive assist for avoiding a collision between the collision object detected by the object detecting section and the own vehicle or mitigates damage to the own vehicle due to the collision, an operation state detecting section for detecting an operation state of the own vehicle, and a timing setting section for setting start timing to start the drive assist by the drive assisting section in accordance with the operation state detected by the operation state detecting section.

This application claims priority to Japanese Patent Application No.2013-102316 filed on May 14, 2013, the entire contents of which arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a collision mitigation apparatus foravoiding collision of a vehicle or mitigating collision damage to thevehicle.

2. Description of Related Art

There is known a collision mitigation apparatus which detects acollision object present in front of a vehicle using a sensor such ascamera or a radar, and performs drive assists including giving an alarmand actuating a brake.

For example, Japanese Patent Application Laid-open No. 2012-103969describes such a collision mitigation apparatus which is designed tocalculate a risk level of collision with a detected obstacle, and give awarning if the calculated risk level is high. This collision mitigationapparatus is capable of giving a warning only when it is necessary.

However, if such drive assists are given to a vehicle driver when thevehicle driver correctly perceives the scene in front of the vehicle anddefinitely understands how the vehicle should be driven, the vehicledriver may be annoyed.

Further, when the vehicle is running on a winding road or a curved road,it may occur that an object outside the road is detected to be acollision object present in front of the vehicle, as a result of whichdrive assists for avoiding a collision are performed unnecessarily,causing the vehicle driver to be annoyed.

SUMMARY

According to an exemplary embodiment, there is provided a collisionmitigation apparatus including:

an object detecting section for detecting a collision object present infront of an own vehicle on which the collision mitigation apparatus ismounted;

a drive assisting section that performs drive assist for avoiding acollision between the collision object detected by the object detectingsection and the own vehicle, or mitigates damage to the own vehicle dueto the collision;

an operation state detecting section for detecting an operation state ofthe own vehicle; and

a timing setting section for setting start timing to start the driveassist by the drive assisting section in accordance with the operationstate detected by the operation state detecting section.

According to the exemplary embodiment, there is provided a collisionmitigation apparatus capable of suppressing drive assist from beingunnecessarily performed to prevent a vehicle driver from being annoyed.

Other advantages and features of the invention will become apparent fromthe following description including the drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a block diagram showing the structure of a PCS (precrashsafety system) as a collision mitigation apparatus according to anembodiment of the invention;

FIG. 2 is a flowchart showing steps of a collision object detectingprocess performed by the PCS;

FIG. 3 is a flowchart showing steps of a method of generating fusiondata performed by the PCS;

FIG. 4 is a flowchart showing steps of a drive assist starting processperformed by the PCS;

FIG. 5 is a diagram for explaining the term of “lap ratio”;

FIG. 6 is a diagram for explaining the term of “offset”;

FIG. 7 is a diagram showing an example of a TTC map;

FIG. 8 is a diagram showing an example of a base table;

FIG. 9 is a diagram showing an example of a correction table; and

FIG. 10 is a diagram showing an example of a base table which definesbase threshold values for each of different values of the lap ratio.

PREFERRED EMBODIMENTS OF THE INVENTION

A PCS (precrash safety system) 1 as a collision mitigation apparatusaccording to an embodiment of the invention is a system mounted on avehicle (may be referred to as the own vehicle hereinafter) to avoidcollision of the own vehicle or mitigate collision damage to the ownvehicle by performing drive assists such as giving a warning oractuating a brake device if there is a high risk of collision betweenthe own vehicle and a collision object. The PCS 1 includes a collisionmitigation controller 10, various sensors 20 and a control object 30(see FIG. 1).

The sensors 20 include a camera sensor 21, a radar sensor 22, a yaw-ratesensor 23 and a wheel speed sensor 24. The camera sensor 21, which is astereo camera capable of range finding in this embodiment, recognizesthe shape of and the distance to a collision object such as apedestrian, an on-road obstacle or a vehicle based on taken images.

The radar sensor 22 emits a directional electromagnetic wave toward acollision object, and receives a reflected version of the directionalelectromagnetic wave to recognize the position of the collision objectrelative to the own vehicle together with its shape and size.

The yaw-rate sensor 23 detects the turning angular velocity of the ownvehicle. The wheel speed sensor 24 detects the wheel rotational speed asthe speed of the own vehicle.

Detection results of these sensors 20 are received by the collisionmitigation controller 10. Incidentally, each of the camera sensor 21 andthe radar sensor 22 performs a process for detecting a collision objectpresent in front of the own vehicle at a predetermined period (100 ms,for example).

The collision mitigation controller 10 includes a Central ProcessingUnit 11, a ROM 12, a RAM 13 and a communication part 14 forcommunication with other devices such as ECUs 50 and 51 mounted on theown vehicle through an in-vehicle LAN 40. The CPU 11 of the collisionmitigation controller 10 executes programs stored in the ROM 12 inaccordance with the detection results received from the sensors 20, tothereby perform various processes explained later.

The collision mitigation controller 10 actuates the control object 30depending on a result of detection of a collision object. The controlobject 30 may be a brake device, a steering device, an actuator fordriving a seat belt device, and a warning device.

Next, an operation of the PCS 1 is explained. The PCS 1 recognizes thetype (vehicle, pedestrian, bike, motorbike, and so on) of a collisionobject in front of the own vehicle together with its relative position,relative speed, size and shape using the camera sensor 21 or the radarsensor 22.

The PCS 1 also estimates a TTC (time to collision) indicating a timeremaining before collision for each detected collision object based onits relative position and relative speed. If the TTC reaches anoperation threshold, the PCS 1 performs various drive assists throughthe control object 30, such as generation of a warning signal, actuationof the brake device, intervention to a steering operation of the vehicledriver, or tensioning of the seatbelts.

The operation threshold is variably set in accordance with the operationstate of the own vehicle, the kind of a collision object, the positionalrelationship between the collision object and the own vehicle, therunning state of the own vehicle, the running environment of the ownvehicle and so on.

The PCS 1 sets the operation threshold such that timing to start driveassist is to be later when the own vehicle is steered not to runstraight compared to when the own vehicle is steered to run straight.Also, the PCS 1 sets the operation threshold such that timing to startdrive assist is set to be later when the blinker of the own vehicle isin operation compared to when the blinker is not in operation.

Next, a collision object detecting process is explained with referenceto the flowchart of FIG. 2. The collision object detecting process isperformed periodically for detecting a collision object present in frontof the own vehicle.

The collision object detecting process begins in step S100 where thecollision mitigation controller 10 causes the radar sensor 22 to emitthe directional electromagnetic wave and receive a reflected version ofthe directional electromagnetic wave. In subsequent step S105, thecollision mitigation controller 10 detects a collision object(s) basedon the received reflected version of the directional electromagneticwave, and calculates the relative position (the distance from the ownvehicle and lateral position relative to the own vehicle) of eachcollision object. Further, the collision mitigation controller 10recognizes the size and shape of each collision object. Thereafter, theprocess proceeds to step S110.

Incidentally, if a collision object once detected has not been detectedby the radar sensor 22, the collision mitigation controller 10 estimatesthe present relative position of this collision object by interpolationof data representing the past relative positions of this collisionobject, as long as the number of continuous cycles in which the radarsensor 2 failed to detect this collision object is smaller than apredetermined number.

In step S110, the collision mitigation controller 10 receives an imagetaken by the camera sensor 21, and then the process proceeds to stepS115. In step S115, the collision mitigation controller 10 performsimage processing on the taken image to extract an area(s) in each ofwhich a collision object is present, and calculates the relativeposition (the distance and direction from the own vehicle) of eachcollision object. Further, the collision mitigation controller 10recognizes the size and shape of each collision object, and determinesthe kind of each collision object by pattern matching or the like.Thereafter, the process proceeds to step S120.

Incidentally, if a collision object once detected has not been detectedby the camera sensor 21, the collision mitigation controller 10estimates the present relative position of this collision object byinterpolation of data representing the past relative positions of thiscollision object, as long as the number of continuous frames in whichthe camera sensor 21 failed to detect this collision objected is smallerthan a predetermined number.

In step S120, the collision mitigation controller 10 calculates fusiondata representing more accurately a relative position (referred to asthe fine position hereinafter) of each collision object based on itsrelative position obtained by the radar sensor 22 and its relativeposition obtained by the camera sensor 21. More specifically, as shownin FIG. 3, the collision mitigation controller 10 sets a straight lineL1 connecting the position of the own vehicle and the relative position200 of a detected collision object determined from its relative distanceand relative direction obtained by the camera sensor 21, and sets astraight line L2 extending laterally from the relative position 210 ofthe collision object determined from its relative distance and relativeposition obtained by the radar sensor 21. The collision mitigationcontroller 10 determines the intersection point of these straight linesL1 and L2 as the fine relative position of the collision object (fusiondata).

Further, the collision mitigation controller 10 sets, as a radardetection area 215, a rectangular area having a predetermined size andcentered around the relative position of the collision object obtainedby the radar sensor 22. Thereafter, the collision mitigation controller10 sets a circular sector area having a predetermined central angle andcentered around the center of the front end of the own vehicle, thecenter line of the circular sector area extending to the direction ofthe relative position of the collision objet obtained by the camerasensor 21, and sets also a band-shaped area which extends laterally andon whose center in the front-back direction the relative position of thecollision object obtained by the camera sensor 21 lies. The collisionmitigation controller 10 sets the overlapped portion between these twoareas as a camera detection area 205.

Subsequently, the collision mitigation controller 10 calculates the areaof the overlapped portion between the radar detection area 215 and thecamera detection area 205. If the calculated area is larger than orequal to a predetermined value, drive assist is carried out depending onthe fusion data representing the fine relative position of the collisionobject.

If the collision object has been detected by only one of the radarsensor 22 and the camera sensor 21, or if the above calculated area issmaller than the predetermined value, drive assist is carried outdepending on the relative position of the collision object obtained bythe radar sensor 22 or the camera sensor 21.

In subsequent step S125, the collision mitigation controller 10calculates the TTC for each collision object by dividing the distancebetween the collision object and the own vehicle by the relative speedof the collision object, for example.

Next, a drive assist starting process for setting start timing to startdrive assist for each collision object and starting drive assist whenthe start timing comes is explained with reference to the flowchart ofFIG. 4. This process is performed periodically.

The drive assist starting process begins in step S300 where thecollision mitigation controller 10 determines whether or not a collisionobject has been detected. If the determination result in step S300 isaffirmative, the process proceeds to step S305, and otherwise isterminated.

In step S305, the collision mitigation controller 10 detects theoperation states of the steering wheel, brake device and blinker of theown vehicle. More specifically, if the amount of variation per unit timeof the yaw rate detected by the yaw rate sensor 23 is larger than apredetermined threshold, the collision mitigation controller 10determines that the steering angle of the own vehicle is wobbling, thatis, a wobbling steering operation is underway.

Further, if the absolute value of the yaw rate remains larger than apredetermined threshold for longer than a predetermined time, thecollision mitigation controller 10 determines that the steering angle ofthe own vehicle is kept at a certain angle larger than a predeterminedthreshold, that is, a constant steering angle operation is underway.

Further, if the increase or decrease amount per unit time of the yawrate is larger than a predetermined value, the collision mitigationcontroller 10 determines that the increase or decrease rate of thesteering angle of the own vehicle exceeds a predetermined threshold,that is, a turning angle increasing operation is underway.

If none of these operations has been detected, the collision mitigationcontroller 10 determines that a straight steering operation is underway.

The output of a steering angle sensor mounted on the own vehicle may beused to detect the above steering operations. Further, depending on datareceived from the ECU 50 and 51, the collision mitigation controller 10determines that a braking operation is underway or a blinking operationis underway.

In subsequent step S310, the collision mitigation controller 10 detectsthe running state of the own vehicle including the vehicle speedmeasured by the wheel speed sensor 24. Further, the collision mitigationcontroller 10 calculates the relative acceleration of each collisionobject relative to the own vehicle using historical records of therelative speed of each collision object. Thereafter, the processproceeds to step S315.

In step S315, the collision mitigation controller 10 calculates thewidth (lateral length) of each collision object based on the size andshape and so on of each collision object. Further, the collisionmitigation controller 10 calculates a lap ratio and an offset of eachcollision object based on the relative position of each collision objectand the kind of each object recognized by the camera sensor 21.

Here, as shown in FIG. 5, the lap ratio is a degree by which the frontend of the own vehicle 400 and the rear end of a vehicle 410 as acollision object laterally overlap with each other. More specifically,the lap ratio may be a ratio of the lateral length of the lateraloverlap between the front end of the own vehicle 400 and the rear end ofthe vehicle 410 to the width of the own vehicle 400.

As shown in FIG. 6, the offset is a degree of lateral deviation betweena pedestrian 430 as a collision object and the lateral center of the ownvehicle 420. More specifically, the offset may be a ratio of the lateraldistance (d) of the lateral center of the own vehicle 420 and thepedestrian 430 to the half of the width of the own vehicle 420.

When a collision object having been detected by the radar sensor 22 isnot detected by the camera sensor 21, the kind of the collision objectmay be determined based on the shape of the collision object recognizedby the radar sensor 22, to calculate the lap ratio and offset.

In step S320, the collision mitigation controller 10 detects the runningenvironment of the own vehicle based on a detection result of the camerasensor 21 or radar sensor 22 and so on. More specifically, the collisionmitigation controller 10 may detect, as the running environment, adetermination result whether the road ahead of the own vehicle is curvedor not based on the output of the camera sensor 21 or the radar sensor22. Also, the collision mitigation controller 10 may detect, as therunning environment, a determination result whether the own vehicle or acollision object is inside a white line painted on the road, or whetherthe own vehicle and the collision object are in the same lane. Further,the collision mitigation controller 10 may detect, as the runningenvironment, a determination result whether the own vehicle is runningin a tunnel or not, or what time of day the own vehicle is running at(daytime, evening or night).

In step S325, the collision mitigation controller 10 sets timing tostart drive assist for each collision object. More specifically, thecollision mitigation controller 10 determines the moving direction ofeach collision object using historical records of relative speed of eachcollision object, and reads the operation threshold for each collisionobject from a TTC map storing the operation thresholds for various kindsof collision objects, each of the operation thresholds having differentvalues for different moving directions, different operation states,different running states and different running environments (to beexplained in detail later).

In subsequent step S330, the collision mitigation controller 10determines whether or not the TTC has reached the operation threshold(that is, whether timing to start drive assist has come or not) for eachcollision object. If the determination result in step S330 isaffirmative, the process proceeds to step S335, and otherwise thisprocess is terminated.

In step S335, the collision mitigation controller 10 controls thecontrol object 30 so that drive assist is started when the timing tostart it has come.

Next, the TTC map is explained. As shown in FIG. 7, the TTC map storesmap data for the operation thresholds for different kinds of driveassist objects, each of the operation thresholds having different valuesfor different operation states, different running states and differentrunning environments.

In this TTC map, the item “STATIONARY OBJECT” means an object at rest ona road. This item is classified into sub-items “VEHICLE” meaning astationary vehicle, “PEDESTRIAN” meaning a stationary pedestrian,“OTHERS” meaning any stationary object other than a vehicle and apedestrian, and “CROSSING” meaning an object moving laterally in frontof the own vehicle.

The item “PRECEDING OBJECT” means an object present in front of the ownvehicle and moving in the same direction as the moving direction of theown vehicle. This item is classified into sub-items “VEHICLE” meaning apreceding vehicle of the own vehicle, and “PEDESTRIAN” meaning apedestrian walking ahead of the own vehicle.

The item “ONCOMING OBJECT” means an object present in front of the ownvehicle and approaching the own vehicle. This item is classified intosub-items “VEHICLE” meaning a vehicle which is in front of the ownvehicle and approaching the own vehicle, and “PEDESTRIAN” meaning apedestrian who is in front of the own vehicle and approaching the ownvehicle.

Further, the TTC map includes items “BASE TABLE”, “OPERATION STATE”,“RUNNING STATE” and “RUNNING ENVIRONMENT”. The item “BASE TABLE”includes base tables “A-1” to “H-1” provided corresponding to the abovedescribed different drive assist objects. Each of these base tablesdefines a relationship between a base threshold used as a basis fordetermining the operation threshold and the relative speed of the driveassist object.

To set the start timing, one of these base tables corresponding to thekind of a detected drive assist object (collision object) is selected,and the base threshold is calculated based on the selected base tableand the relative speed of the drive assist object.

Further, each of the items “OPERATION STATE”, “RUNNING STATE” and“RUNNING ENVIRONMENT” includes correction tables (“A-2” to ““H-2”, . . .“A-10” to “H-10”. As shown in FIG. 9, Each of these correction tablesshows a relationship between a correction value and the relative speedof a corresponding one of the drive assist objects.

To set the start timing, one or more of the correction tables whichcorresponds to the present operation state, running state, runningenvironment and the kind of the detected drive assist object is selectedfrom the TTC map, and the correction value corresponding to the relativespeed is read from the selected correction table. When two or more ofthe collection tables are selected, the sum of the correction valuesread from these tables is calculated as a combined correction value.

The operation threshold is calculated to be the sum of the basethreshold and the correction value. When two or more of the collectiontables are selected, the operation threshold is calculated to be the sumof the base threshold and the combined correction value. As shown inFIG. 7, the item “OPERATION STATE” is classified into sub-items“STRAIGHT STEERING OPERATION”, “WOBBLING STEERING OPERATION”, “CONSTANTSTEERING OPERATION”, “TURNING ANGLE INCREASING OPERATION”, “BRAKINGOPERATION” and “BLINKING OPERATION”. These sub-items are providedcorresponding to the respective states detected in step S305.

One or more of these sub-items which corresponds to the detectedoperation state(s) is selected, and the correction table(s)corresponding to the selected sub-item(s) is selected.

As described in the foregoing, the PCS 1 is configured to set theoperation threshold such that timing to start drive assist is later whenthe own vehicle is steered not to run straight compared to when the ownvehicle is steered to run straight. Accordingly, the correction valuesdefined by the correction tables corresponding to the sub-items“WOBBLING STEERING OPERATION”, “CONSTANT STEERING ANGLE OPERATION” and“TURNING ANGLE INCREASING OPERATION” are smaller than the correctionvalue defined by the correction table corresponding to the sub-item“STRAIGHT STEERING OPERATION”.

Further, as described in the foregoing, the PCS 1 is configured to setthe operation threshold such that timing to start drive assist is latewhen a braking operation or a blinking operation is underway compared towhen they are not underway. Accordingly, the correction values definedby the correction tables corresponding to the sub-items “BRAKINGOPERATION” and “BLINKING OPERATION” are negative.

As shown in FIG. 7, the item “RUNNING STATE” of the TCC map includes asub-item “RELATIVE SPEED≦X” which means a running state in which therelative acceleration between the own vehicle and the drive assistobject is greater than or equal to a predetermined threshold value. Whenthe own vehicle is in such a running state, the correction tablecorresponding to this sub-item and the kind of the drive assist objectis selected.

Other than the above described correction tables, a correction table fora running state in which the relative speed between the own vehicle andthe drive assist object is greater than or equal to a predeterminedthreshold value may be provided. As shown in FIG. 7, the item “RUNNINGENVIRONMENT” of the TCC map is classified into sub-terms “CURVE AHEAD”meaning that the road ahead of the own vehicle is curved and “WHITE LINERECOGNIZED” meaning that the own vehicle and the drive assist object arein the same lane. When the running environment of the own vehicle is thesame as any one of these states, a corresponding correction table isselected.

The base tables and correction tables corresponding to the sub-item“VEHICLE” may be prepared so as to define the relationship between thebase threshold and the relative speed for each of different values ofthe lap ratio, or a relationship between the correction value and therelative speed for each of different values of the lap ratio. Further,the base tables and correction tables corresponding to the sub-item“PEDESTRIAN” may be prepared so as to define the relationship betweenthe base threshold and the relative speed for each of different valuesof the offset, or a relationship between the correction value and therelative speed for each of different values of the offset.

In these cases, the relationship between the base threshold and therelative speed for a given value of the lap ratio with the drive assistobject (vehicle), or the relationship between the correction value andthe relative speed for a given value of the offset with the drive assistobject (pedestrian) may be determined using the selected base table orcorrection table. Thereafter, the base threshold or correction value maybe determined from the determined relationship.

FIG. 10 shows an example of the base table which shows a relationshipbetween the base threshold and the relative speed for each of differentranges of the lap ratio. In the base table of this example, arelationship between the base threshold and the relative speed aredefined for each of the lap ratio ranges of 0% to 20%, 20% to 50% and50% to 100%. According to this base table, since the base thresholddecreases with the decrease of the lap ratio for the same relativespeed, the start timing is set to be later when the lap ratio is lowcompared to when the lap ratio is high.

The TTC map may include a base table which defines a relationshipbetween the base threshold and the relative speed for each of differentranges of the offset. The different ranges of the offset may include arange of 0 to ¼, a range of ¼ to ½ and a range of ½ to 1.

In this case, the base threshold for a case where the offset is small(or where the distance between a collision object and the lateral centerof the own vehicle is small) maybe set large compared to a case wherethe offset is large (or where the distance between the collision objectand the lateral center of the own vehicle is large) for the samerelative speed, so that the start timing is set to be later when theoffset is large compared to when the offset is small.

The correction tables corresponding to the sub-item “VEHICLE” may beprepared so as to define the correction values differently for differentvalues of the lap ratio. Likewise, the correction tables correspondingto the sub-item “PEDESTRIAN” may be prepared so as to define thecorrection values differently for different values of the offset.

The above described embodiment of the present invention provides thefollowing advantages. According to the PCS 1, when a wobbling steeringoperation or a constant steering angle operation or a steering angleincreasing operation is underway, the drive assist start timing is setto be late.

Accordingly, when an object outside the road comes to be located infront of the own vehicle as a result of performing such steeringoperations, and is detected to be a collision object, since unnecessarydrive assist can be suppressed, it is possible to prevent excessiveannoyance caused to the vehicle driver.

When a braking operation or a blinking operation is underway, it can beassumed that the vehicle driver is correctly perceiving the environmentand driving the own vehicle appropriately.

According to the PCS 1 of the above embodiment, since timing to startdrive assist is set to be later in such situation, it is possible toprevent the vehicle driver from being annoyed too much when the vehicledriver drives the own vehicle with appropriate intention and purpose.

The PCS 1 of this embodiment sets the TTC for each of detected collisionobjects based on their relative positions relative to the own vehicle,and performs drive assist if the TTC reaches the operation threshold foreach of the respective collision objects. The operation threshold is setin accordance with the operation state, running state and runningenvironment of the own vehicle so that the drive assist start timing canbe set appropriately.

When a detected collision object is a vehicle, the operation thresholdis set in accordance with the lap ratio between this vehicle and the ownvehicle. When a detected collision object is a pedestrian, the operationthreshold is set in accordance with the offset between this pedestrianand the own vehicle. Hence, according to this embodiment, it is possibleto set the drive assist start timing appropriately depending on thepositional relationship between the own vehicle and a detected collisionobject.

Other Embodiments

(1) The PCS 1 of the above embodiment is configured to detect acollision object using both the camera sensor 21 and the radar sensor22. However, the PCS1 may be configured to detect a collision objectusing one of the camera sensor 21 and the radar sensor 22, or using asensor other than a radar and a camera.

(2) The TCC map may be prepared differently for different destinations(regions or countries) where the PCS 1 is used. Further, the TCC map maybe prepared differently for different vehicle types or sizes.

The PCS 1 may be configured to select among from different TCC maps inaccordance with its destination or type or size of a vehicle using thePCS 1.

Correspondence between the above described embodiment and the claims:

The object detecting section corresponds to steps S100 to S120. Theoperation state detecting section corresponds to step S305. The runningstate detecting section corresponds to step S310. The object detectingsection corresponds to step S315. The timing setting section correspondsto step S325. The drive assisting section corresponds to step S335.

The above explained preferred embodiments are exemplary of the inventionof the present application which is described solely by the claimsappended below. It should be understood that modifications of thepreferred embodiments may be made as would occur to one of skill in theart.

What is claimed is:
 1. A collision mitigation apparatus comprising: acollision mitigation controller including a central processing unit(CPU) that: detects a collision object present in front of an ownvehicle on which the collision mitigation apparatus is mounted anddetermines a type of the collision object from a plurality of prescribedtypes of collision objects; actuates a control object to perform driveassist for avoiding a collision between the collision object detected bythe collision mitigation controller and the own vehicle or mitigatingdamage to the own vehicle due to the collision; determines which ofprescribed operation states the own vehicle is in; sets a start timingto start the drive assist by the collision mitigation controller inaccordance with the operation state detected by the collision mitigationcontroller; and map data including a base table provided correspondingto each of the plurality of prescribed types of collision objects, inwhich a base threshold for setting the start timing for each of theplurality of prescribed types of collision objects is stored, and acorrection table provided corresponding to each of the prescribedoperation states, in which a correction value for setting the starttiming for each of the prescribed operation states is stored; a camerasensor for taking an image ahead of the own vehicle and a radar sensorconfigured to emit electromagnetic waves ahead of the own vehicle andreceive a reflected version of the electromagnetic waves, the collisionmitigation controller being configured to set an area centered around aposition of the collision object obtained by the camera sensor as acamera detection area and to set a predetermined area centered around aposition of the collision object obtained by the radar sensor as a radardetection area; the collision mitigation controller being configured todetect the collision object and determine the type of the collisionobject using both the camera sensor and the radar sensor when an area ofan overlapped portion between the camera detection area and the radardetection area exceeds a predetermined value, and otherwise detect thecollision object and determine the type of the collision object usingone of the camera sensor and the radar sensor; wherein the collisionmitigation controller sets the start timing based on the base thresholdread from the base table corresponding to the determined type of thecollision object, and the correction value read from the correctiontable corresponding to the determined operation state; and wherein, whenthe collision mitigation controller detects the collision object anddetermines the type of the collision object using both the camera sensorand the radar sensor, the collision mitigation controller determines theposition of the collision object based on a direction to the collisionobject from the own vehicle detected by the camera sensor and a distanceto the collision object from the own vehicle in a front-back directionof the own vehicle detected by the radar sensor.
 2. The collisionmitigation apparatus according to claim 1, wherein the collisionmitigation controller sets the start timing to be later when thecollision mitigation controller detects that the own vehicle is in anot-straight running state where the own vehicle is operated so as notto run straight compared to when the collision mitigation controllerdetects that the own vehicle is in a straight running state where theown vehicle is operated so as to run straight.
 3. The collisionmitigation apparatus according to claim 2, wherein the collisionmitigation controller determines that the own vehicle is in thenot-straight running state if an amount of variation per unit time of asteering angle of the own vehicle exceeds a predetermined threshold, orthe steering angle exceeds a predetermined threshold, or an increase ordecrease rate of the steering angle exceeds a predetermined threshold.4. The collision mitigation apparatus according to claim 1, wherein thecollision mitigation controller sets the start timing to be later whenat least one of a blinker of the own vehicle and a brake device of theown vehicle is in operation compared to when neither of the blinker andthe brake device is in operation.
 5. The collision mitigation apparatusaccording to claim 1, wherein the collision mitigation controllerdetects a running state of the own vehicle, the collision mitigationcontroller being configured to set the start timing taking into accountthe running state of the own vehicle detected by the collisionmitigation controller.
 6. The collision mitigation apparatus accordingto claim 1, wherein the collision mitigation controller detects apositional relationship between the own vehicle and the collisionobject, the collision mitigation controller being configured to set thestart timing taking into account the positional relationship detected bythe collision mitigation controller.
 7. The collision mitigationapparatus according to claim 6, wherein the collision mitigationcontroller detects, as the positional relationship, a distance in alateral direction between the own vehicle and the collision object, andthe collision mitigation controller sets the start timing taking intoaccount the distance in the lateral direction between the own vehicleand the collision object.
 8. The collision mitigation apparatusaccording to claim 6, wherein the collision mitigation controllerdetects a lateral positional relationship between the own vehicle andthe collision object and a lateral length of the collision object, thecollision mitigation controller being configured to set the start timingtaking into account the lateral positional relationship and the laterallength detected by the collision mitigation controller.
 9. The collisionmitigation apparatus according to claim 8, wherein the collisionmitigation controller determines a degree by which the own vehicle andthe collision object overlap with each other in a lateral directionbased on the lateral positional relationship between the own vehicle andthe collision object and the lateral length of the collision object, andsets the start timing taking into account the degree.